This invention relates to a polyvinyl chloride sheet and to blood bags, and infusion bags made therefrom, the surfaces of which are modified so that the diffusion of plasticizer to the surface is suppressed and compatibility of the polyvinyl chloride with respect to the contents of the bags is improved.
It is well known that crosslinked thin layers on the surfaces of chlorine-containing vinyl polymers such as polyvinyl chloride and polyvinylidene chloride, formed by glow discharge or UV radiation, act as barriers to migration of lower molecular weight substances such as monomers, plasticizers and additives to the surface. This surface modification method is considered to be very useful, because hardening of said resins and environmental contamination caused by diffusion and release of the plasticizer are serious defects.
However we have found during our study of this type of surface modification that the modified surface becomes rough and loses transparency to polarized light when the polyvinyl chloride sheet with a thin crosslinked layer is heated above its softening point. The transparency of the sheet is a very important property for many applications. For example, if medical bags such as blood bags and infusion bags lose transparency during the heating process involved in autoclave sterilization or during the process of ethylene oxide gas sterilization, the contents of the bag cannot substantially be observed through the bag. An important object of this invention is to provide a transparent polyvinyl chloride sheet having a high quality crosslinked thin layer on its surface.
At present, many blood bags are made of polyvinyl chloride sheet because of its flexibility and other well-balanced properties. However, the compatibility problem and the decrease of numbers and activities of platelets that is encountered during the preservation still remain unsolved. This invention provides blood bags having improved use as preservatives of platelets through the use of specific gases during glow discharge, and through the use of specific anticoagulation agents. Therefore, the creation of polyvinyl chloride sheets and blood bags made therefrom, having improved biocompatibility, is another important object of this invention.
Usually a plastic surface treated by glow discharge becomes hydrophilic (good wettability), which can be a valuable or a detrimental property, depending on the intended application. For the use of blood bags and infusion bags, a reduced diffusion rate of water is preferable. The glow discharge treatments heretofore carried out have not resulted in low diffusion rates. Furthermore, we have encountered a serious problem in that emulsified lipids contained in a high calorie infusion increase in size due to interaction between the emulsion and the hydrophilic surface treated by ordinary glow discharge. A further object of this invention is to provide a modified polyvinyl chloride sheet which retards the diffusion of the plasticizer and whose surface is hydrophobic.
Other objects of this invention will appear in further detail hereinafter and in the following description.